Steam circuits of steam plants can include different temperature regions wherein higher temperature regions can be made of materials with higher heat strength that can be more expensive than lower heat strength materials used in lower temperature regions. Due to a difference in cost between materials of differing heat strength, it can be advantageous to reduce the temperature in high temperature branches, such as steam turbine bypasses, of the steam circuit.
GB patent application No. 2 453 849 A discloses the use of a water injection cooler for reducing the temperature exposure in a branch. The cooler functions by spraying water in the branch so that it comes in direct contact with the steam to be cooled. While this can be effective in reducing steam temperature to the point where lower temperature alloys may be used, the disclosed system uses a steam flow to operate and therefore cannot be universally applied to branches with no flow modes, such as bypasses, bleeds or vent lines and still ensure low temperature in the branch during all operating modes.
As an alternative, IPCOM000176170D discloses injecting an inert gas in a branch that acts as a heat buffer during no flow modes of operation. When the branch is, for example, a turbine bypass, the change from no flow to flow mode may result in the inert gas entering the steam circuit. Unless removed with additional equipment, the inert gas can have a negative affect on steam turbine efficiency. In addition, this does not address the thermal shock that may occur when the branch is brought into flow mode from a no flow mode, as the method is not able ensure an adequate temperature is maintained in the branch.
An alternative is to provide external heating and cooling elements over the branch piping and associated equipment. While such arrangements are physically possible such solutions can add significant complexity and cost to the steam plant.